The present invention generally relates to delivering and injecting fluid into heart tissue. More specifically, the present invention relates to delivering and injecting fluid into heart tissue utilizing needle-less injection.
Injection catheters may be used to inject therapeutic or diagnostic agents into a variety of organs, such as the heart. In the case of injecting a therapeutic agent into the heart, 27 or 28 gauge needles are generally used to inject solutions carrying genes, proteins, or drugs directly into the myocardium. A typical volume of an agent delivered to an injection site is about 100 microliters. One limitation to this method of delivering therapeutic agents to the heart is that the injected fluid tends to leak from the site of the injection after the needle is disengaged from the heart. In fact, fluid may continue to leak over several seconds. In the case of dynamic organs such as the heart, there may be more pronounced leakage with each muscle contraction. A second limitation to this method is that the injected fluid remains as a bolus at the injection site and is not distributed over a very wide area. A third limitation is that needles leave more permanent trauma.
Therapeutic and diagnostic agents may be delivered to a portion of the heart as part of a percutaneous myocardial revascularization (PMR) procedure. PMR is a procedure which is aimed at assuring that the heart is properly oxygenated. Assuring that the heart muscle is adequately supplied with oxygen is critical to sustaining the life of a patient. To receive an adequate supply of oxygen, the heart muscle must be well perfused with blood. In a healthy heart, blood perfusion is accomplished with a system of blood vessels and capillaries. However, it is common for the blood vessels to become occluded (blocked) or stenotic (narrowed). A stenosis may be formed by an atheroma which is typically a harder, calcified substance which forms on the walls of a blood vessel.
Historically, individual stenotic lesions have been treated with a number of medical procedures including coronary bypass surgery, angioplasty and atherectomy. Coronary bypass surgery typically involves utilizing vascular tissue from another part of the patient""s body to construct a shunt around the obstructed vessel. Angioplasty techniques such as percutaneous transluminal angioplasty (PTA) and percutaneous transluminal coronary angioplasty (PTCA) are relatively non-invasive methods of treating a stenotic lesion. These angioplasty techniques typically involve the use of a guide wire and a balloon catheter. In these procedures, a balloon catheter is advanced over a guide wire such that the balloon is positioned proximate a restriction in a diseased vessel. The balloon is then inflated and the restriction in the vessel is opened. A third technique which may be used to treat a stenotic lesion is atherectomy. During an atherectomy procedure, the stenotic lesion is mechanically cut or abraded away from the blood vessel wall.
Coronary by-pass, angioplasty and atherectomy procedures have all been found effective in treating individual stenotic lesions in relatively large blood vessels. However, the heart muscle is perfused with blood through a network of small vessels and capillaries. In some cases, a large number of stenotic lesions may occur in a large number of locations throughout this network of small blood vessels and capillaries. The torturous path and small diameter of these blood vessels limit access to the stenotic lesions. The sheer number and small size of these stenotic lesions make techniques such as cardiovascular by-pass surgery, angioplasty, and atherectomy impractical.
When techniques which treat individual lesion are not practical, percutaneous myocardial revascularization (PMR) may be used to improve the oxygenation of the myocardial tissue. A PMR procedure generally involves the creation of holes, craters or channels directly into the myocardium of the heart. In a typical PMR procedure, these holes are created using radio frequency or laser energy delivered by a catheter having one or more electrodes near its distal end. After the wound has been created, therapeutic agents are sometimes injected into the heart chamber from the distal end of a catheter.
Positive clinical results have been demonstrated in human patients receiving PMR treatments. These results are believed to be caused, in part, by blood flowing within the heart chamber through channels in myocardial tissue formed by PMR. Increased blood flow to the myocardium is also believed to be caused, in part, by the healing response to wound formation. Specifically, the formation of new blood vessels is believed to occur in response to the newly created wound. This response is sometimes referred to as angiogenesis. After the wound has been created, therapeutic agents which are intended to promote angiogenesis are sometimes injected into the heart chamber. A limitation of this procedure is that the therapeutic agent may be quickly carried away by the flow of blood through the heart.
In addition to promoting increased blood flow, it is also believed that PMR improves a patient""s condition through denervation. Denervation is the elimination of nerves. The creation of wounds during a PMR procedure results in the elimination of nerve endings which were previously sending pain signals to the brain as a result of hibernating tissue.
Currently available injection catheters are not particularly suitable for accurately delivering small volumes of therapeutic agents to heart tissue. Improved devices and methods are desired to address the problems associated with retention of the agent in the heart tissue as discussed above. This is particularly true for agents carrying genes, proteins, or other angiogenic drugs which may be very expensive, even in small doses.
The present invention provides an improved apparatus and method for delivering and injecting fluid into heart tissue. The present invention addresses the problems associated with retention of the fluid in the heart tissue and disbursement of the fluid throughout a wider tissue area by utilizing high pressure needle-less injection. The present invention may be used to deliver genes, proteins or drugs directly into the myocardium for purposes of myocardial revascularization. The present invention provides an improved apparatus and method for causing transient trauma that may stimulate angiogenesis.
In an exemplary embodiment, the present invention provides a catheter system including an injection catheter connected to a pressurized fluid source capable of generating a high transient pressure sufficient to pierce tissue. The injection catheter includes an elongate shaft defining an infusion lumen in fluid communication with the fluid contained in the pressurized fluid source. The distal end of the shaft includes a nozzle having an injection port in fluid communication with the infusion lumen such that fluid from the pressurized fluid source may be delivered to the heart tissue at a sufficiently high exit velocity to partially penetrate the heart tissue.
To accommodate the relatively high pressures involved, the shaft of the injection catheter may be formed of a metal or a reinforced polymer composite to withstand the pressure burst. The injection port may have a small diameter in the range of 0.001 to 0.05 inches, depending on the desired injection parameters, such as exit velocity, volume delivered, target tissue area, etc. The injection port may be larger or smaller than the lumen in the nozzle in order to change the exit velocity adjacent the port. In addition, the nozzle may be sharpened in order to partially penetrate the heart tissue.
The present invention also provides a method of delivering a fluid to heart tissue including the steps of: providing a pressurized fluid source and an injection catheter substantially as described above; inserting the injection catheter into the patient; navigating the catheter until the distal end of the catheter is positioned adjacent the injection site; and actuating the fluid source to inject fluid into the heart tissue via the infusion lumen of the shaft and the injection port at a sufficient exit velocity to partially penetrate the heart tissue.
By utilizing high pressure needle-less injection, the present invention reduces trauma as compared to needle based systems. In addition, the high pressure needle-less injection system of the present invention reduces fluid leakage from the injection site and distributes injected fluid over a greater volume of tissue.